This invention relates to a member of nylon 12 which is possessed of excellent extrusion moldability, as well as excellent creep characteristics and fatigue characteristics, and to a method for its production.
This invention relates to a nylon 12 composition which is possessed of excellent extrusion moldability and excellent flexibility, creep characteristics and low temperature impact strength. Said nylon 12 and said nylon 12 composition can be used for mainly extrusion molds such as tubular molds, sheet molds, and monofilaments, and is particularly suited for tubular molds.
Since nylon 12 has high chemical resistance, heat resistance and dimensional stability at the time of water absorption, it has been used as a material for injection moldings and for extrusion molds such as tubes, sheets and films in various industrial fields. In recent years, development of the use of nylon 12 has been making progress in the field of tubular molds such as fuel tubes, various hoses for industrial use, and gas pipes, and characteristics of nylon 12 required in this field have been highly advanced and diversified. Particularly, a demand has been increasing for a material for use in tubes, which has good moldability and shows excellent durability under severe environment, namely a member of nylon 12 which is possessed of excellent extrusion moldability, as well as excellent creep characteristics and fatigue characteristics.
With regard to the improvement of moldability of nylon 12, JP-A-7-278294 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), for example, discloses a method for the production of a member of nylon 12 which has excellent melt fluidity and is suited for precision molding. This type of nylon 12 is characterized in that its relative viscosity (to be referred to as xe2x80x9cxcex7rxe2x80x9d hereinafter) and melt flow rate (to be referred to as xe2x80x9cMFRxe2x80x9d hereinafter) have a specific relationship. JP-A-7-278294 relates mainly to precision molding or the like injection molding. In general, injection molding shows a tendency in that the moldability becomes good as the melt fluidity of a polymer becomes superior, namely as the melt viscosity becomes low. In the case of the molding of tubes and the like extrusion moldings, however, too low melt viscosity causes a difficulty in obtaining tubular moldings having proper shapes because of the difficulty in keeping the tube shapes at the time of molding. Because of this, when the nylon 12 having superior melt fluidity disclosed in JP-A-7-278294 was used, there was limitation on molding conditions for obtaining proper tubular moldings. In order to produce good extrusion moldings stably, nylon 12 having a melt fluidity different from the case of injection molding was required. Because of this, development of nylon 12 suitable for extrusion molding is expected.
In addition, no prior art information is available concerning the improvement of creep characteristics and fatigue characteristics of nylon 12. It is said in general that the durability-related characteristics such as creep characteristics and fatigue characteristics of a polymer become excellent as its molecular weight is increased. There are some proposals concerning methods for increasing molecular weight of polyamide. For example, JP-A-3-97732 discloses a method in which a polyamide having relatively low molecular weight is mixed with a phosphorus compound under a melting condition and made into pellet, powder or the like shape and then its molecular weight is increased by solid phase polymerization. However, it is difficult to produce nylon 12 having a xcex7r value of 5 or more even by the use of this method. Creep characteristics and fatigue characteristics of nylon 12 having a xcex7r value of about 5 are not sufficient when compared with the intended values of the present invention. Also, being extremely low in melt fluidity, it was difficult to use nylon 12 having a xcex7r value of 5 in extrusion molding. Because of this, concern has been directed toward the development of nylon 12 which has excellent extrusion moldability, creep characteristics and fatigue characteristics and is suitable as a tube material.
On the other hand, with the expansion of the range of their use, a demand has been increasing for nylon 12 which can be used under an environment where temperature changes widely or at a low temperature, e.g., xe2x88x9240xc2x0 C. However, flexibility, low temperature impact strength, durability-related creep characteristics and the like properties of the prior art nylon 12 were not satisfactory for its use under such severe environment.
With regard to the method for improving flexibility and low temperature impact strength of nylon 12, proposals have been made for example on a composition which comprises nylon 12 and a plasticizer having good compatibility and a composition which comprises a polyamide resin, a plasticizer, a modified polyolefin and/or a thermoplastic elastomer.
With regard to the composition comprising a polyamide and a plasticizer, JP-A-62-283151, for example, discloses polyamide resin molds having flexibility which comprise nylon 12 and the like and 2-ethylhexyl-p-hydroxy benzoate as a plasticizer. Also, JP-A-1-185362 discloses a composition which comprises a polyamide resin and an ester as a plasticizer obtained from p-hydroxybenzoic acid and a branched alcohol having 12 to 22 carbon atoms.
However, according to these proposals, impact strength at a low temperature of for example xe2x88x9230xc2x0 C. or below was not sufficient and the creep characteristics was also insufficient, though flexibility was improved.
Also, with regard to the composition comprising a polyamide resin, a plasticizer and a modified polyolefin, JP-A-5-320504 discloses a composition which comprises a nylon 12 resin, a modified polyolefin composed of an olefin mainly consisting of ethylene and/or propylene and an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof, and a plasticizer such as an ester synthesized for example from p-hydroxybenzoic acid and a branched alcohol having 12 to 22 carbon atoms. In addition, JP-A-8-325451 discloses tubular molds which comprise nylon 12, a modified polyolefin composed of an olefin mainly consisting of ethylene and/or propylene and an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof and a plasticizer. These proposed compositions were not satisfactory in terms of their creep characteristics, though their flexibility and low temperature impact strength were improved.
The object of the present invention is to provide a member of nylon 12 which is possessed of excellent extrusion moldability, as well as excellent creep characteristics and fatigue characteristics, and a method for its production.
Another object of the present invention is to provide a nylon 12 composition which has excellent flexibility, low temperature impact strength and creep characteristics.
The inventors of the present invention have examined in detail on the relationship between basic physical properties of nylon 12 and its extrusion moldability, creep characteristics and fatigue characteristics and found as a result of the efforts that a member of nylon 12 in which its relative viscosity (xcex7r) and melt flow rate (MFR) values have a specific relationship shows excellent extrusion moldability and its creep characteristics and fatigue characteristics become excellent too, thus resulting in the accomplishment of the present invention.
Moreover, the inventors of the present invention have examined in detail on the effects of physical properties of nylon 12 and kinds of plasticizer on the flexibility, low temperature impact strength and creep characteristics of nylon 12 and found as a result of the efforts that a composition prepared by adding a specified plasticizer and, as occasion demands, a modified polyolefin to nylon 12 in which its xcex7r and MFR have a specific relationship can show excellent flexibility, low temperature impact strength and creep characteristics, thus resulting in the accomplishment of the present invention.
These objects of the present invention are accomplished by the following third aspects.
The first aspect of the present invention is a member of nylon 12 having a xcex7r value of from 1.9 to 3.5 when measured in 98% sulfuric acid at a concentration of 10 g/dm3 and at 25xc2x0 C. and a MFR value of 0.1 g/10 min. or more when measured at 235xc2x0 C. under a load of 2,160 g, wherein said xcex7r value and said MFR value have a relationship of the following formula (I):
2.87xc3x97103 exp(xe2x88x923.48 xcex7r)xe2x89xa6MFRxe2x89xa63.25xc3x97104 exp(xe2x88x923.48 xcex7r)xe2x80x83xe2x80x83(I) 
wherein xcex7r is relative viscosity and MFR is melt flow rate.
The second aspect of the present invention is a method for the production of the nylon 12 described as the first aspect, which comprises carrying out a pre-polymerization step under pressure melting condition and a subsequent post-polymerization step under ordinary pressure or a reduced pressure, wherein polymerization temperature of the pre-polymerization step is set within the range of from 270 to 320xc2x0 C., and the polymerization temperature, pressure inside the polymerization system and polymerization time in the pre-polymerization step are controlled keeping a relationship of the following formula (II):
7.99xc3x97105 exp(xe2x88x922.19xc3x9710xe2x88x922 T)xe2x89xa7Ptxe2x89xa75.64xc3x97107 exp(xe2x88x924.24xc3x9710xe2x88x922 T)xe2x80x83xe2x80x83(II) 
wherein T is polymerization temperature and its unit is xc2x0 C., P is pressure inside the polymerization system and its unit is kgf/cm2 G, and t is polymerization time and its unit is hour (hr).
The third aspect of the present invention is a nylon 12 composition which comprises (A) 100 parts by weight of nylon 12 having a xcex7r value of from 1.9 to 3.5 when measured in 98% sulfuric acid at a concentration of 10 g/dm3 and at 25xc2x0 C. and a MFR value of 0.1 g/10 min. or more when measured at 235xc2x0 C. under a load of 2,160 g, wherein said xcex7r and said MFR have a relationship of the formula (I):
2.87xc3x97103 exp(xe2x88x923.48 xcex7r)xe2x89xa6MFRxe2x89xa63.25xc3x97104 exp(xe2x88x923.48 xcex7r)xe2x80x83xe2x80x83(I) 
wherein xcex7r is relative viscosity and MFR is melt flow rate, (B) from 1 to 25 parts by weight of a plasticizer, and (C) from 0 to 30 parts by weight of a modified polyolefin obtained from an olefin consisting of ethylene and/or propylene as the main component and an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof.
It is well known that xcex7r and MFR of polymers are physical properties which exert influences upon moldability. However, nothing is known about the relationship between the xcex7r and MFR values of nylon 12 and the extrusion moldability. In addition, it is not known that a member of nylon 12 having a specific relationship between xcex7r and MFR is excellent in creep characteristics and fatigue characteristics, which was found for the first time by the present invention.
The present invention is characterized by the finding that a composition comprising nylon 12 having a specific relationship between its xcex7r and MFR values and a plasticizer, or a composition in which a modified polyolefin is added to the former composition as occasion demands, has excellent flexibility, low temperature impact strength and creep characteristics.
The following describes the present invention in detail.
The nylon 12 of the present invention is produced from xcfx89-laurolactam and/or xcfx89-aminododecanoic acid as the main component. Though the nylon 12 of the present invention can be produced from xcfx89-laurolactam or xcfx89-aminododecanoic acid alone, their copolymerized products with other lactams, aminocarboxylic acids, or polyamide-forming diamines and dicarboxylic acids or nylon salts composed thereof are also included in the present invention, with the proviso that they are 30% by weight or less of xcfx89-laurolactam and/or xcfx89-aminododecanoic acid.
Specific examples of the other lactam to be copolymerized include xcex1-pyrrolidone, xcex5-caprolactam, xcfx89-enantholactum, xcex1-piperidone, xcfx89-undecanlactam and the like. Illustrative examples of the other aminocarboxylic acid include 6-aminocapronic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminocapric acid, 11-aminoundecanoic acid and the like.
Specific examples of the polyamide-forming diamine include tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 1,3-diaminocyclohexane, m-xylylenediamine, p-xylylenediamine and the like.
Specific examples of the polyamide-forming dicarboxylic acid include adipic acid, suberic acid, azelaic acid, sebacic acid, nonanedionic acid, decanedionic acid, undecanedionic acid, dodecanedionic acid, 1,2-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and the like. These diamines and dicarboxylic acids are used in almost the same molar basis. Also, the nylon salt composed of such diamine and dicarboxylic acid is an equimolar salt of the diamine and dicarboxylic acid.
The other lactams, aminocarboxylic acids, or polyamide-forming diamines and dicarboxylic acids or nylon salts composed thereof to be used as the aforementioned copolymer components may be used alone or by optionally combining two or more of them, with the proviso that they are 30% by weight or less of xcfx89-laurolactam and/or xcfx89-aminododecanoic acid.
The nylon 12 of the present invention has a xcex7r value of from 1.9 to 3.5, preferably from 2.1 to 3.3, and a MFR value of 0.1 g/10 min. or more, and the xcex7r and MFR have the relationship represented by the formula (I).
When xcex7r is larger than 3.5, the melt fluidity becomes poor which causes a difficulty in obtaining tubular molds, sheets and the like extrusion molds having excellent appearances. Also, when xcex7r is smaller than 1.9, the melt fluidity may be excellent, but it becomes difficult to obtain satisfactory tubular molds because of poor shape-keeping ability of the extrusion molds at the time of extrusion molding. It also causes a problem of entailing poor creep characteristics and fatigue characteristics. In this connection, xcex7r is a value to be used as a scale of the molecular weight of nylon 12, which is measured using Ubbelohde viscometer in 98% sulfuric acid at a concentration of 10 g/dm3 and at 25xc2x0 C.
When MFR is smaller than 0.1 g/10 min., the extrusion moldability becomes extremely poor to causes a difficulty in obtaining tubular molds, sheets and the like extrusion molds having excellent appearances. In this connection, MFR is a value measured at 235xc2x0 C. under a load of 2,160 g, and its unit is g/10 min.
In addition, when xcex7r and MFR are within the aforementioned ranges but the relationship between xcex7r and MFR deviates from the range of the formula (I), extrusion moldability in tube molding and the like may be good, but creep characteristics and fatigue characteristics become poor.
The nylon 12 of the present invention can be produced by any production method, with the proviso that its xcex7r and MFR have the aforementioned specific relationship. In consequence, a known polyamide producing apparatus can be used in the production of the nylon 12 of the present invention by either a batch or continuous production method. Examples of the apparatus eligible for use in the production include a batch type reaction vessel, a single or multiple vessel type continuous reaction apparatus, a tubular continuous reaction apparatus, a kneading reaction extruder and the like.
In a preferred production method of the nylon 12 of the present invention, a pre-polymerization step is carried out by using xcfx89-laurolactam and/or xcfx89-aminododecanoic acid as monomers, if necessary adding water, a copolymerization component, a molecular weight adjusting agent and the like, and effecting ring-opening reaction and initial condensation polymerization under a melting and high or ordinary pressure conditions, and then a post-polymerization step is carried out to increase the molecular weight by effecting condensation polymerization under a melting and ordinary or a reduced pressure conditions. This method can be carried out either by a continuous system or a batch system.
The following illustratively describes a preferred example of the production method of the nylon 12 of the present invention, using xcfx89-laurolactam as the starting material.
The pre-polymerization is carried out using predetermined amounts of xcfx89-laurolactam and water at a polymerization temperature of from 270 to 320xc2x0 C., preferably from 280 to 310xc2x0 C., under an increased pressure and under such conditions that the polymerization temperature T, the pressure inside the polymerization system (to be referred to as xe2x80x9csystem pressurexe2x80x9d hereinafter in some cases) P and the polymerization time t have a relationship of the following formula (II):
7.99xc3x97105 exp(xe2x88x922.19xc3x9710xe2x88x922 T)xe2x89xa7Ptxe2x89xa75.64xc3x97107 exp(xe2x88x924.24xc3x9710xe2x88x922 T)xe2x80x83xe2x80x83(II) 
wherein unit of the polymerization temperature T is xc2x0 C., unit of the pressure P inside the polymerization system is kgf/cm2 G, and unit of the polymerization time t is hour (hr). In this connection, the system pressure means mainly pressure of water vapor inside the polymerization reaction system.
The nylon 12 obtained by the pre-polymerization has a xcex7r of from 1.01 to 1.8, preferably from 1.1 to 1.6. A xcex7r value of smaller than 1.01 is not desirable, because it will prolong polymerization time of the post-polymerization step. After completion of the pre-polymerization, the nylon 12 of the present invention can be produced by carrying out post-polymerization for a predetermined period of time under ordinary pressure or a reduced pressure at a temperature of from 230 to 350xc2x0 C., preferably from 240 to 320xc2x0 C.
System pressure and polymerization time at the time of the post-polymerization are optionally decided depending on the xcex7r value of nylon 12 to be produced. In general, the system pressure at the time of post-polymerization is from 10 Torr to ordinary pressure, and the polymerization time is 5 minutes or more.
When polymerization temperature of the pre-polymerization step is lower than 270xc2x0 C., it becomes difficult to produce the nylon 12 of the present invention having the aforementioned specific relationship between xcex7r and MFR, and the productivity is reduced due to prolonged pre-polymerization time. On the other hand, when it is higher than 320xc2x0 C., side reaction and deterioration reaction are apt to occur at the time of polymerization, so that it becomes difficult to produce the nylon 12 of the present invention having the aforementioned specific relationship between xcex7r and MFR, and coloring of the produced nylon 12 occurs. Also, when the relationship between the product of system pressure and polymerization time and the polymerization temperature does not satisfy the aforementioned formula (II) in the pre-polymerization step, it becomes difficult to produce the nylon 12 of the present invention having the aforementioned specific relationship between xcex7r and MFR.
When temperature at the time of the post-polymerization is lower than 230xc2x0 C., it becomes difficult to produce the nylon 12 of the present invention having the aforementioned specific relationship between xcex7r and MFR, and the post-polymerization time is prolonged. On the other hand, when it is higher than 350xc2x0 C., side reaction and deterioration reaction are apt to occur at the time of polymerization, so that it becomes difficult to produce the nylon 12 of the present invention having the aforementioned specific relationship between xcex7r and MFR, and coloring of the produced nylon 12 occurs.
In producing the nylon 12 of the present invention, phosphorus compounds such as phosphoric acid, phosphorous acid, hydrophosphorous acid, pyrophosphoric acid, polyphosphoric acid or their alkali metal salts, alkaline earth metal salts and esters may be added as occasion demands, in order to accelerate polymerization or prevent deterioration at the time of polymerization. The amount of these phosphorus compounds to be added is within the range of from 50 to 3,000 ppm based on the nylon 12 to be produced.
As occasion demands, an amine, a carboxylic acid and the like may be added for the purpose of controlling molecular weight of the nylon 12 of the present invention or stabilizing its melt viscosity. Monofunctional and/or bifunctional amines and carboxylic acids can be used. Specific examples of the amine include laurylamine, stearylamine, benzylamine, 1,6-diaminohexane, 1,9-diaminononane, 1,11-diaminoundecane, 1,12-diaminododecane, m-xylylenediamine, p-xylylenediamine and the like.
Specific examples of the carboxylic acid include acetic acid, benzoic acid, lauric acid, stearic acid, butanedionic acid, hexanedionic acid, isophthalic acid, terephthalic acid and the like. The amount of these amines and carboxylic acids to be added is optionally decided depending on the r value of the nylon 12 to be produced.
The nylon 12 composition which comprises (A) nylon 12 of the present invention and (B) a plasticizer is a composition necessary for achieving the object of the present invention. Also, a composition which comprises (A) nylon 12 of the present invention, (B) a plasticizer and (C) a modified polyolefin is another composition necessary for achieving the object of the present invention.
In the nylon 12 composition of the present invention, the plasticizer (B) to be used in the present invention is at least one compound selected from esters and alkylamides. The terms xe2x80x9cestersxe2x80x9d as used herein means phthalic acid esters, fatty acid esters, polyhydric alcohol esters, phosphoric acid esters, trimellitic acid esters and hydroxybenzoic acid esters. Specific examples of phthalic acid esters include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate, ditridecyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate, diisononyl phthalate, ethylphthalylethyl glycolate, butylphthalylbutyl glycolate, diundecyl phthalate, di-2-ethylhexyl tetrahydrophthalate and the like.
Specific examples of fatty acid esters include dibasic saturated carboxylic acid esters such as dimethyl adipate, dibutyl adipate, diisobutyl adipate, dibutyldiglycol adipate, di-2-ethylhexyl adipate, di-n-octyl adipate, diisodecyl adipate, diisononyl adipate, an adipic acid di-n-mixed alkyl ester, dimethyl sebacate, dibutyl sebacate, di-2-ethylhexyl sebacate, di-2-ethylhexyl azelate, a di-2-ethylhexyl mixed acid ester and bis-2-ethylhexyl didodecanoate, and dibasic unsaturated carboxylic acid esters such as dibutyl fumarate, bis-2-methylpropyl fumarate, bis-2-ethylhexyl furarate, dimethyl maleate, diethyl maleate, dibutyl maleate and bis-2-ethylhexyl maleate, as well as butyl oleate, isobutyl oleate, acetylbutyl recinolate, tributyl acetylcitrate, 2-ethylhexyl acetate and the like.
Specific examples of polyhydric alcohol esters include 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, diethylene glycol dibenzoate, triethylene glycol di-2-ethylbutyrate, pentaerythritol monooleate, pentaerythritol monostearate, pentaerythritol trialkyl ester, behenic acid monoglyceride, 2-ethylhexyl triglyceride, glycerol triacetate, glycerol tributyrate and the like.
Specific examples of phosphoric acid esters include trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, tributoxyethyl phosphate, triphenyl phosphate, n-octyldiphenyl phosphate, cresyldiphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, 2-ethylhexyldiphenyl phosphate and the like.
Specific examples of trimellitic acid esters include tributyl trimellitate, tri-2-ethylhexyl trimellitate, tri-n-octyl trimellitate, triisononyl trimellitate, triisodecyl trimellitate, a trimellitic acid tri-mixed alcohol ester and the like.
Specific examples of hydroxybenzoic acid esters include ethylhexyl o- or p-hydroxybenzoate, hexyldecyl o- or p-hydroxybenzoate, ethyldecyl o- or p-hydroxybenzoate, octyloctyl o- or p-hydroxybenzoate, decyldodecyl o- or p-hydroxybenzoate, methyl o- or p-hydroxybenzoate, butyl o- or p-hydroxybenzoate, hexyl o- or p-hydroxybenzoate, n-octyl o- or p-hydroxybenzoate, decyl o- or p-hydroxybenzoate, dodecyl o- or p-hydroxybenzoate and the like.
The alkylamides are toluenesulfonic acid alkylamides or benzenesulfonic acid alkylamides. Specific examples of toluenesulfonic acid alkylamides include N-ethyl-o-toluenesulfonic acid butylamide, N-ethyl-p-toluenesulfonic acid butylamide, N-ethyl-o-toluenesulfonic acid 2-ethylhexylamide, N-ethyl-p-toluenesulfonic acid 2-ethylhexylamide and the like. Specific examples of benzenesulfonic acid alkylamides include benzenesulfonic acid propylamide, benzenesulfonic acid butylamide, benzenesulfonic acid 2-ethylhexylamide and the like. These plasticizers cited above may be used alone or by optionally combining two or more of them.
Among these plasticizers, phthalic acid esters such as dibutyl phthalate, diisodecyl phthalate and di-2-ethylhexyl phthalate, hydroxybenzoic acid esters such as ethylhexyl p-hydroxybenzoate and hexyldecyl p-hydroxybenzoate, and alkylamides such as benzenesulfonic acid butylamide and benzenesulfonic acid 2-ethylhexylamide are preferably used.
The modified polyolefin (C) to be used in the nylon 12 composition of the present invention as occasion demands is a block copolymer, a random copolymer or a graft copolymer which is obtained by copolymerizing an olefin consisting of ethylene and/or propylene as the main component with an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof. The modified polyolefin is synthesized by using an olefin monomer or polymer comprising ethylene and/or propylene as the main component. Specific examples of the copolymer of an olefin comprising ethylene and/or propylene as the main component (to be referred to as xe2x80x9cpolyolefinxe2x80x9d hereinafter in some cases) include an ethylene-propylene copolymer, an ethylene-1-butene copolymer, an ethylene-1-hexene copolymer, an ethylene-4-methylpentene-1 copolymer, an ethylene-1-decene copolymer, an ethylene-1-dodecene copolymer and the like copolymers of ethylene with one or two or more xcex1-olefins, and an ethylene-butylene-styrene copolymer, an ethylene-propylene-styrene copolymer, a styrene-ethylene-butylene-styrene copolymer, a styrene-ethylene-propylene-styrene copolymer and the like. Among these polyolefins, an ethylene-propylene copolymer, an ethylene-butylene-styrene copolymer, an ethylene-propylene-styrene copolymer, a styrene-ethylene-butylene-styrene copolymer and the like are preferably used.
Among these polyolefins, those which use ethylene as the main component having the ethylene content of generally from 30 to 90 mol %, preferably from 40 to 90 mol %, are used most preferably in view of the effect to improve flexibility and low temperature impact strength. When the ethylene content of these polyolefins is less than 30 mol %, glass transition temperature of the polyolefin becomes high so that the effect to improve low temperature impact strength becomes insufficient. Also, when it exceeds 90 mol %, crystallinity of these polyolefins becomes high so that the elastic property is lost and the flexibility and low temperature impact strength are reduced.
Specific examples of the xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof to be copolymerized with a polyolefin comprising ethylene and/or propylene as the main component include monobasic unsaturated carboxylic acids such as acrylic acid, methacrylic acid, methyl methacrylate, crotonic acid and isocrotonic acid, dibasic unsaturated carboxylic acids such as maleic acid, fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, endo-cis-bicyclo[2,2,1]hepto-5-ene-2,3-dicarboxylic acid, or derivatives of these monobasic or dibasic unsaturated carboxylic acids such as maleic anhydride, nadic anhydride, itaconic anhydride and the like acid anhydrides, acid halide, amide, imide, sodium salt, zinc salt and the like.
Block copolymers or random copolymers which are obtained by copolymerizing a polyolefin comprising ethylene and/or propylene as the main component with an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof can be produced by known olefin polymerization methods using a polyolefin comprising ethylene and/or propylene as the main component and an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof as the starting materials.
The xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof is used preferably in an amount of from 0.01 to 30 mol % based on the polyolefin.
In the case of graft polymerization, there are known methods such as a method in which the aforementioned polyolefin comprising ethylene and/or propylene as the main component is melted or dissolved in a solvent, an xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof and a radical generator are added to the thus melted or dissolved material and then the resulting mixture is heated with stirring to effect graft polymerization. Among these methods, a method in which graft polymerization of the aforementioned xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof to a melted polyolefin is carried out using an extruder is most simple and efficient. In carrying out graft polymerization, graft polymers can be produced efficiently when a radical generator such as an organic peroxide or an azo compound is used. Examples of the radical generator include an organic peroxide, an organic per-ester and an azo compound. Specific examples of the organic peroxide, organic per-ester and the like include benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, cyclohexanone peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(peroxide benzoate)hexyne-3,1,4-bis(tert-butylperoxyisopropyl)benzene, lauroyl peroxide, tert-t-butyl peracetate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl perbenzoate, tert-butyl perphenylacetate, tert-butyl perisobutyrate, tert-butyl per-sec-octoate, tert-butyl perpivalate, cumyl perpivalate, tert-butyl perdiethylacetate and the like. Specific examples of the azo compound include azobisisobutyronitrile, dimethyl azoisobutyrate and the like.
Amount of the xcex1,xcex2-unsaturated carboxylic acid or a derivative thereof to be used in the graft polymerization is generally within the range of from 0.02 to 6% by weight based on the polyolefin comprising ethylene and/or propylene as the main component. If its amount does not fall within this range, it would cause poor miscibility with nylon 12 and therefore entail insufficient impact strength at low temperature.
When the nylon 12 composition of the present invention consists essentially of (A) nylon 12 of the present invention and (B) a plasticizer, their amounts to be blended are (A) 100 parts by weight of nylon 12 of the present invention and (B) from 1 to 25 parts by weight, preferably from 3 to 20 parts by weight, of the plasticizer. If the amount of the plasticizer is smaller than the lower limit, it would bear no sufficient effect to improve flexibility and low temperature impact strength. On the other hand, if the amount is larger than the upper limit, it would cause reduction of creep characteristics and heat resistance.
When the nylon 12 composition of the present invention consists essentially of (A) nylon 12 of the present invention, (B) a plasticizer and (C) a modified polyolefin, their amounts to be blended are (A) 100 parts by weight of nylon 12 of the present invention, (B) from 1 to 25 parts by weight, preferably from 3 to 20 parts by weight, of the plasticizer and (C) from more than 0 to 30 parts by weight, preferably from 1 to 25 parts by weight, more preferably from 3 to 25 parts by weight, of the modified polyolefin. If the amount of the modified polyolefin (C) is smaller than the just described lower limit, it would bear no sufficient effect to improve low temperature impact strength. On the other hand, if the amount is larger than the upper limit, it would cause reduction of creep characteristics.
Within such a range that the purpose of the present invention is not spoiled, the nylon 12 of the present invention or the nylon 12 composition of the present invention may be blended with an antioxidant such as a phenol-based, thioether-based, phosphite-based or amine-based compound; a heat resistance stabilizer such as an organic tin-based, lead-based or metal soap-based compound; a weather resistance improving agent such as a salicylate-based, benzophenone-based, benzotriazole-based, cyanoacrylate-based or metal complex salt-based ultraviolet ray absorbing compound; an anti-static agent such as an alkylamine, an alkylamide, an alkyl ether, an alkylphenyl ether, a glycerol fatty acid ester, a sorbitan fatty acid ester, an alkyl sulfonate, an alkylbenzene sulfonate, an alkyl sulfate, an alkyl phosphate, a quaternary ammonium salt or an alkylbetaine; an inorganic flame retardant such as red phosphorus, tin oxide, zirconium hydroxide, barium metaborate, aluminum hydroxide or magnesium hydroxide; an organic flame retardant such as a halogen-based, phosphoric ester-based, melamine-based or cyanuric acid-based compound; and a flame retardant assisting agent such as antimony trioxide; as well as a nucleating agent, an oil, a pigment, a dye and the like.
The method for obtaining the nylon 12 composition of the present invention is not particularly limited, and various well known methods can be used. Examples of such applicable methods include a method in which predetermined amounts of (A) nylon 12 of the present invention, (B) a plasticizer and, as occasion demands, (C) a modified polyolefin, as well as various additives, are mixed in advance using a V type blender, a tumbler or the like low rotation mixer or Henschel mixer or the like high rotation mixer, melt-kneaded using a single screw extruder, a twin screw extruder or a twin screw kneader and then made into pellets, and a method in which predetermined amounts of nylon 12 of the present invention (A) and, as occasion demands, a modified polyolefin (C) are mixed in advance using the just described low rotation mixer or high rotation mixer, melt-kneaded using a single screw extruder, a twin screw extruder or a twin screw kneader while injecting a plasticizer (B) into the cylinder of the melt kneader and then made into pellets. In this connection, it is desirable to employ the latter method when the plasticizer (B) is liquid at room temperature.
Since the nylon 12 of the present invention or the nylon 12 composition of the present invention is possessed of excellent moldability, particularly excellent extrusion moldability, it can be applied suitably to tubular molds, and extrusion molds of films, fibers, monofilaments and the like, and particularly suitable for fuel tubes, various tubes in the automobile engine room, gas pipes and the like tubular molds. These tubular molds are produced for example by using a general single screw extruder equipped with a straight die for tube use and a sizing former, carrying out the extrusion at a cylinder temperature of from the melting point of the nylon 12 of the present invention to 330xc2x0 C., usually from 190 to 280xc2x0 C., preferably from 200 to 280xc2x0 C., and then cooling the extruded product with water or the like.
In addition, the nylon 12 of the present invention or the nylon 12 composition of the present invention can also be applied to the production of blow molds and deep-drawn box-like molds not only by extrusion molding but also by injection molding, blow molding, vacuum molding and the like well known molding methods.